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United States Patent |
5,726,575
|
Poittevin
,   et al.
|
March 10, 1998
|
Path for acquiring a voltage pulse, and a method and a system for
measuring partial discharges and provided with such a path
Abstract
The invention relates to an acquisition path for acquiring a voltage pulse,
and to a system and a method making use of said path, the path comprises:
a path input for a pulse signal;
a module for determining the polarity and for limiting acquisition of the
input signal;
a control module for controlling acquisition and for storing the polarized
peak value of the input signal;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired, and for holding it; and
selection means for selecting the rating of the signal being acquired;
according to the invention the selection module for selecting the rating of
the signal being acquired comprises a plurality of measurement ranges all
of which are connected at their upstream ends to the path input, and all
of which are connected at their downstream ends to automatic selection
means for automatically selecting the optimum measurement range for the
signal being acquired.
Inventors:
|
Poittevin; Jean (Courbevoie, FR);
Ryadi; Mohamed (Le Mans, FR);
Bonnet; Jean-Claude (Gouaix, FR);
Mazankine; Jacques (Gouaix, FR)
|
Assignee:
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GEC Alsthom T & D SA (Paris, FR)
|
Appl. No.:
|
522920 |
Filed:
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September 1, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
324/536; 324/544; 324/601 |
Intern'l Class: |
G01R 031/00 |
Field of Search: |
324/536,541,544,551
364/551.01
|
References Cited
U.S. Patent Documents
3421076 | Jan., 1969 | Eigen | 324/544.
|
3602706 | Aug., 1971 | Levitt | 364/551.
|
3777259 | Dec., 1973 | Clinton | 324/601.
|
3861780 | Jan., 1975 | Ross | 364/551.
|
4663586 | May., 1987 | Swerlein | 324/601.
|
4757263 | Jul., 1988 | Cummings et al. | 324/552.
|
4780661 | Oct., 1988 | Baloney et al. | 324/601.
|
5047725 | Sep., 1991 | Strid et al. | 324/601.
|
5247258 | Sep., 1993 | Tripier et al. | 324/54.
|
5256976 | Oct., 1993 | Ishikawa et al. | 324/544.
|
5319311 | Jun., 1994 | Kawashima et al. | 324/544.
|
5477150 | Dec., 1995 | Ham, Jr. et al. | 324/536.
|
5514967 | May., 1996 | Zelm | 324/551.
|
Foreign Patent Documents |
0205312 | Dec., 1983 | DE | 324/536.
|
2034140 | May., 1990 | GB.
| |
WO9001704 | Feb., 1990 | WO.
| |
Primary Examiner: Regan; Maura K.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas, PLLC
Claims
We claim:
1. A path for acquiring a voltage pulse measured in an electrical
apparatus, said path comprising:
a path input for a pulse signal detected at a measurement point of said
electrical apparatus;
a module for determining polarity and for limiting acquisition to detect
the polarity of the input signal and to limit pulse acquisition to input
signals exceeding predetermined threshold values;
a control module for controlling acquisition and storage of the polarized
peak value of the input signal if the input signal exceeds the
predetermined threshold values;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired and for holding it during a predetermined given
length of time; and
a selection module for selecting a measurement range for measuring the
signal being acquired, the selection module having a plurality of
measurement ranges, all connected at their upstream ends to the input of
the path, and all connected at their downstream ends to automatic
selection means for automatically selecting the measurement range which is
optimum for the signal in acquisition.
2. An acquisition path according to claim 1, wherein each measurement range
includes a detect-and-hold module.
3. An acquisition path according to claim 1, wherein each measurement range
includes an amplifier of known gain and of known saturation voltage, the
automatic selection means including means for scanning the plurality of
measurement ranges in order of decreasing amplifier gain, and means for
selecting the first non-saturated measurement range in scan order.
4. An acquisition path according to claim 3, wherein the detect-and-hold
module is located downstream from the amplifier and upstream from the
automatic selection means.
5. An acquisition path according to claim 1, wherein the detect-and-hold
module comprises analog detect-and-hold means connected in series with
digitizing means for digitizing the detected polarized peak value.
6. An acquisition path according to claim 1, including a storage module for
storing the detected polarized peak value as selected and made available
at the output of the automatic selection means.
7. An acquisition path according to claim 1, including adjustment means for
adjusting the predetermined threshold values, and controllable selection
means for selecting the measurement range to be connected to the module
for determining polarity and for limiting acquisition.
8. A system for measuring partial discharges in an electrical apparatus,
the system comprising:
at least one acquisition path comprising:
a path input for a pulse signal detected at a measurement point of said
electrical apparatus;
a module for determining polarity and for limiting acquisition to detect
the polarity of the input signal and to limit pulse acquisition to input
signals exceeding predetermined threshold values;
a control module for controlling acquisition and storage of the polarized
peak value of the input signal if the input signal exceeds the
predetermined threshold values;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired and for holding it during a predetermined given
length of time; and
a selection module for selecting a measurement range for measuring the
signal being acquired, the selection module having a plurality of
measurement ranges, all connected at their upstream ends to the input of
the path, and all connected at their downstream ends to automatic
selection means for automatically selecting the measurement range which is
optimum for the signal in acquisition;
a reference path for digitizing and storing the polarized feed voltage of
the electrical apparatus synchronously with the acquisition path; and
a transfer module for transferring to a common archive file located in a
microcomputer or equivalent, the digital polarized peak values as stored
in the storage module of the acquisition path, together with the
associated feed polarized voltage as stored in the reference path.
9. A system according to claim 8, including means for processing the data
in the common file and display means and means for outputting said data or
the results of processing said data.
10. A system according to claim 8, comprising seven acquisition paths and
one reference path, each acquisition path having four measurement ranges
which in combination provide a dynamic measurement range of about one to
one million.
11. A method of measuring partial discharges and of processing said
measurements using a measurement system comprising:
at least one acquisition path comprising:
a path input for a pulse signal detected at a measurement point of said
electrical apparatus;
a module for determining polarity and for limiting acquisition to detect
the polarity of the input signal and to limit pulse acquisition to input
signals exceeding predetermined threshold values;
a control module for controlling acquisition and storage of the polarized
peak value of the input signal if the input signal exceeds the
predetermined threshold values;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired and for holding it during a predetermined given
length of time; and
a selection module for selecting a measurement range for measuring the
signal being acquired, the selection module having a plurality of
measurement ranges, all connected at their upstream ends to the input of
the path, and all connected at their downstream ends to automatic
selection means for automatically selecting the measurement range which is
optimum for the signal in acquisition;
a reference path for digitizing and storing the polarized feed voltage of
the electrical apparatus synchronously with the acquisition path; and
a transfer module for transferring to a common archive file located in a
microcomputer or equivalent, the digital polarized peak values as stored
in the storage module of the acquisition path, together with the
associated feed polarized voltage as stored in the reference path;
wherein several acquisition paths are connected to measurement points
selected in the electrical apparatus, and
the reference path is connected to one of the feed voltages of the
electrical apparatus;
for each acquisition path, the method comprising the steps of:
making an input signal available for the acquisition path, and distributing
this signal among all of the measurement ranges and via the controllable
selection means in the module for determining polarity and limiting
acquisition;
using the module for determining polarity and limiting acquisition to
determine the polarity of the signal and compare the value of the signal
with the threshold values, and when said threshold values are exceeded,
generating a trigger command applied to all of the detect-and-hold modules
and to the control module which starts a time delay using the shift means;
during the time delay, using the detect-and-hold modules to detect the peak
value of the signal by using the analog means;
during the time delay, or at the end thereof, using the control module to
generate an acquisition command for the reference path which then
acquires, digitizes, and stores the number of the period and the polarized
value of the reference voltage at said instant;
at the end of the time delay, causing the control module to control the
digitizing means to digitize the peak value of the signal;
using the automatic selection means to scan the measurement ranges in order
of decreasing gain, and to select the first digitized value which is below
the saturation threshold of the measurement range from which it is
delivered;
operating the control module to cause the selected value to be stored in
the storage module, and then to reset the modules to zero to wait for a
new signal; and
transferring the data collected in this way into the common file for
archive purposes and/or for post-treatment purposes.
12. A method according to claim 11, wherein the transfer step takes place
at the end of a measurement campaign lasting a given time.
13. A method according to claim 11, wherein the transfer step takes place
during a measurement campaign, in idle periods during which no discharge
is being detected.
Description
The invention relates to a path for acquiring a voltage pulse, and to a
method of measuring partial discharges implemented in a system for
measuring partial discharges, the system including at least one such path.
BACKGROUND OF THE INVENTION
Partial discharges take place, in particular, in equipment used in high
tension installations in networks for transporting or distributing
electricity. A partial discharge is a dielectric breakdown phenomenon that
occurs in a portion only of the insulation between two conductors without
giving rise to total breakdown of the components concerned.
The signature of a partial discharge at various points in the apparatus
that has suffered the discharge can provide information concerning the
aging of certain components. As a result, analysis of such signatures can
considerably improve predictive maintenance means, particularly in high
tension electricity installations.
Single-path systems are known for acquiring partial discharges that enable
an average to be obtained of the partial discharges detected over a
half-period of the reference voltage. If it is desired to perform high
quality predictive maintenance, it is necessary to obtain a partial
discharge signature that is more accurate. Averaging over a half-period
gives rise to losses of information.
In the single-path acquisition systems described above, the received
signals are rated manually. Unfortunately, a partial discharge may
generate pulse signals over an extremely wide range of amplitudes, running
from a few millivolts to a few hundreds of volts. In addition, the pulses
last for a few microseconds. As a result manual rating of the signals is
not effective. If the lower threshold of the chosen rating is too high,
then certain signals of lower amplitude are not detected, and if the upper
threshold is too low, then information concerning signals of larger
amplitude is erroneous. In addition, manual adjustment requires the
continuous presence of an extremely vigilant operator.
Finally, those apparatuses are single-path apparatuses. Unfortunately, if
predictive maintenance is to be effective, the signature of a partial
discharge needs to be picked up from a plurality of measurement points and
the resulting information cross-checked. With such apparatuses, it is
therefore necessary to use as many single-path apparatuses as there are
measurement points.
Multipath systems are known for measuring partial discharges that enable
the latter drawback to be overcome. One such system is described in FR-A-2
635 192.
That system comprises a plurality of paths, each having:
a path input for a pulse signal detected at a measurement point of said
electrical apparatus;
a module for determining polarity and for limiting acquisition to detect
the polarity of the input signal and to limit pulse acquisition to input
signals exceeding predetermined threshold values;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired and for holding it during a predetermined given
length of time; and
a control module.
All of the paths are connected to a computer or equivalent via a common
multiplexer interface which digitizes the results of acquisition on each
of the paths, one after another.
That system does not allow for any rating to be performed. Information is
therefore lost if the rating of the path does not enable certain signals
of low amplitude to be detected, and information is erroneous for signals
of large amplitude that saturate the rating.
In addition, the use of a single digitizing device for all of the paths via
a multiplexer, leads to data storage times that are too long, thereby
increasing the minimum time required to perform a measurement on a path.
This increase in time can give rise to measurement of a discharge being
lost if the discharge takes place while a measurement is being performed.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide paths having automatic
modules for performing rating in such a manner that for a given single
amplitude, the module selects the optimum measurement rating.
Another object of the present invention is to make the paths independent
with respect to digitizing and data storage so as to reduce the time
required to perform a measurement.
Another object of the present is to provide a multipath measurement system
and a method enabling a series of measurements to be subjected to
post-treatment without simultaneously interrupting the measurements that
are taking place.
To this end, the invention relates to a path for acquiring a voltage pulse
that is measured in an electrical apparatus. The path comprises:
a path input for a pulse signal detected at a measurement point of said
electrical apparatus;
a module for determining polarity and for limiting acquisition to detect
the polarity of the input signal and to limit pulse acquisition to an
input signal exceeding predetermined threshold values;
a control module for controlling acquisition and storage of the polarized
peak value of the input signal if the input signal exceeds the
predetermined threshold values;
a detect-and-hold module for detecting the polarized peak value of the
signal being acquired and for holding it during a predetermined given
length of time; and
a selection module for selecting the rating of the signal being acquired.
According to the invention, the selection module for selecting the rating
of the signal being acquired comprises a plurality of measurement ranges,
all connected at their upstream ends to the input of the path, and all
connected at their downstream ends to the automatic selection means for
automatically selecting the measurement range which is optimum for the
signal being acquired. Automatic optimum measurement calibration is thus
made possible on the input signal.
Each measurement range includes a detect-and-hold module.
According to the invention, each measurement range includes an amplifier of
known gain and of known saturation voltage, the automatic selection means
including means for scanning the plurality of measurement ranges in order
of decreasing amplifier gain, and means for selecting the first
non-saturated measurement range in scan order.
The detect-and-hold module is located downstream from the amplifier and
upstream from the automatic selection means in each measurement range.
The detect-and-hold module comprises analog detect-and-hold means connected
in series with digitizing means for digitizing the detected polarized peak
value and held.
The acquisition path of the invention includes a storage module for storing
the detected polarized peak value as selected and made available at the
output of the selection module.
Advantageously, the path of the invention includes adjustment means for
adjusting the predetermined threshold values, and controllable selection
means for selecting the measurement range to be connected to the module
for determining polarity and for limiting pulse acquisition.
The invention also provides a system for measuring partial discharges in an
electrical apparatus, the system comprising:
at least one acquisition path as described above;
a reference path for digitizing and storing the polarized feed voltage of
the electrical apparatus; and
a transfer module for transferring to a common archive file located in a
microcomputer or equivalent, the digitized polarized peak values as stored
in the storage module of the acquisition path, together with the
associated feed polarized voltage as stored in the reference path.
The microcomputer or equivalent includes means for processing the data in
the common file and display means and means for outputting said data or
the results of processing said data.
Advantageously, the system comprises seven acquisition paths and one
reference path, each acquisition path having four measurement ranges
which, in combination, provide a dynamic measurement range of about one to
one million.
Finally, the invention also provides an acquisition method in which:
the acquisition paths are connected to the selected measurement points in
the electrical apparatus;
the reference path is connected to one of the feed voltages of the
electrical apparatus;
a signal appears at the input of the acquisition path. This signal is
distributed to all of the measurement ranges and, via the controllable
selection means, to the module for determining polarity and for limiting
acquisition.
The module for determining polarity and for limiting acquisition determines
the polarity of the signal, and compares the value of the signal with
threshold values, and if the threshold values are exceeded, it generates a
trigger command which is applied to all of the detect-and-hold modules,
and also to the control module which begins a time delay by using the
shift means.
During this time delay, the detect-and-hold modules have enough time to
detect the peak value of the signal by using analog means. At the end of
the time delay, the control module activates the digitizing means to cause
them to digitize the peak value of the signal.
During the time delay, or at the end of it, the control module generates an
acquisition command for the reference path. This path acquires, digitizes,
and stores the number of the period and the polarized value of the
reference voltage at that instant.
The automatic selection means scans the measurement ranges in order of
decreasing gain, and it selects the first digitized value that is below
the saturation threshold for the measurement range from which it is
delivered.
The control module then causes the selected value to be stored, and then
activates reinitialization of the modules to wait for a new signal.
A first advantage of the present invention is automatic rating of the input
signal by means of the selection module. Thus, each acquisition is
properly rated and no longer constitutes a potential vector for erroneous
information. In addition, this automatic module does not require any
operator.
Another advantage of the present invention is having a respective
digitizing device integrated within each path. This considerably increases
acquisition speed. Each path can digitize and store its own data
independently of the other paths.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and characteristics of the present invention appear from
the following description given with reference to the accompanying
drawings, in which:
FIG. 1 is a block diagram of a path of the invention;
FIG. 2 is a diagram showing the outside face of a control panel for a path
of the invention;
FIG. 3 is a block diagram of a system of the invention; and
FIGS. 4A, 4B, 4C, and 4D are diagrams giving examples of how data can be
displayed both before and after processing in accordance with the
invention.
MORE DETAILED DESCRIPTION
The path 1 of the invention comprises a path input 4 for a pulse signal
detected at a measurement point on an electrical apparatus.
This path input 4 is connected to the input of a selection module 8 for
selecting the rating of the signal being acquired.
The output of the selection module 8 is connected firstly to the input of a
module 5 for determining polarity and limiting acquisition to determine
the polarity of the input signal and to limit pulse acquisition to an
input signal exceeding predetermined threshold values, and secondly to the
input of a storage module 14 for storing parameters relating to the
acquired signal.
The output of the module 5 for determining polarity and limiting
acquisition is connected firstly to a control input of at least one
detect-and-hold module 7 to detect the polarized peak value of the signal
being acquired and to hold said value during a given length of time, and
secondly to the internal input of a control module 6 for controlling
acquisition and storage of the polarized peak value of the input signal if
the input signal exceeds the predetermined threshold values.
The output of the control module 6 is connected to the control inputs of
the storage module 14, and to the control inputs of at least one
digitizing module 13 for digitizing the detected polarized peak value, and
it has an external input/output 41.
The storage module has an external input/output 40.
Advantageously, the input 4 includes a reactance circuit for fixing the
input impedance of the path, the high cutoff frequency of the passband,
and for providing voltage protection for the downstream circuits.
The selection module 8 for selecting the rating appropriate to the signal
being acquired comprises a plurality of measurement ranges 9 all of which
are connected, upstream, to the path input 4, and downstream to automatic
selection means 10 for automatically selecting the optimum measurement
range 9 for the signal being acquired.
Each measurement range 9 includes its own detect-and-hold module 7.
Each measurement range 9 also includes at least one amplifier 11 of known
gain and of known saturation voltage, and the automatic selection means
comprise means for scanning the plurality of measurement ranges 9 in
decreasing order of amplification gain, and means for selecting the first
non-saturated measurement range 9 in scan order.
The detect-and-hold module 7 is advantageously located downstream from the
amplifier 11 and upstream from the automatic selection means 10.
The detect-and-hold module 7 comprises analog detect-and-hold means 12
controlled by the module 5 for determining polarity and for limiting
acquisition, and connected in series therewith, and a digitizing module 13
controlled by the control module 6.
Each digitizing module 13 is connected to the automatic selection means 10,
said automatic selection means 10 being connected to the input of the
storage module 14.
All of the outputs from the amplifiers 11 are also connected to
controllable selection means 16 of the module 5 for determining polarity
and for limiting acquisition. This selection means is controllable
manually or by program. It selects one of the amplified signals. This
controllable selection means is connected to the inputs of a set of two
comparators 21 and of two bistables 22 that enable the polarity of the
input signal to be determined, and that enable pulse acquisition to be
limited to an input signal that exceeds the predetermined threshold
values.
The module 5 for determining polarity and for limiting acquisition also
includes means 15 for adjusting the threshold values and connected to the
reference terminals of the comparators 21. The control outputs of the
bistables are connected firstly to the internal input of the control
module 6 and secondly to the control input of each of the detect-and-hold
modules 12.
The control module 6 comprises shift means 25 for enabling the
detect-and-hold modules 12 to detect peak values; means for controlling
the digitizing modules 13; and means for controlling the storage module
14.
The control module 6 may also include its own processor. In the embodiment
shown, the control module 6 is synchronized by an external processor
connected to the external input of the control module 6.
The storage module conventionally comprises a memory 23 and a memory
address generator 24 under the control of the control module 6. It further
includes an external output for transferring stored data.
Advantageously, the path 1 includes a display module 17, 18, 19, and 20
that comprises, by way of non-limiting examples, means 17 for indicating
that threshold values have been exceeded, means 18 for displaying the
selected range, means 19 for displaying the amplitude of the signal in the
selected range, and means 20 for displaying polarity.
The invention also includes a system for measuring partial discharges in an
electrical apparatus.
Said system comprises: at least one path 1 as described above; a reference
path 50 for digitizing and storing a polarized reference voltage of the
electrical apparatus which may, by way of non-limiting example, be one of
the power supply voltages of the electrical apparatus; and a transfer
module 43 for transferring the polarized peak values as selected and
stored in the storage module 14, and the associated data relating to the
polarized reference voltage during acquisition into a common archive and
post-treatment file located in a microcomputer 49 or equivalent. Each
acquisition path 1 gives rise to a common file for archiving and
post-treatment. The data contained in the file comprises, by way of
non-limiting example, the amplitude of each detected discharge, its
polarity, and its position in time, i.e. relative to the reference voltage
(number of the reference period, and value of the reference voltage at the
time of the pulse). The transfer means may be activated after each
measurement, or at the end of a series of measurements (a measurement
campaign), or whenever activity is low (no signal) on the path in
consideration.
The reference path 50 comprises:
a reference input 47 connected to a reference voltage;
a module 46 for determining polarity and for limiting acquisition;
a module 44 for detecting, holding and digitizing the polarized reference
voltage;
a module 45 for counting the periods of the reference voltage;
a storage module 48 for storing the digitized polarized reference together
with the number of the associated period;
the set of modules in the reference path being caused to acquire the
reference value by any of the acquisition paths 1 at the moment when the
acquisition path 1 is itself acquiring a polarized peak value of a
discharge.
The transfer module comprises a data bus 51 connected to the memories 23
and 48 of the paths 1 and 50, together with a control bus 52 for selecting
the path to be put into communication with the microcomputer 49 or
equivalent.
The microcomputer 49 or equivalent comprises processing means, display
means, and means for outputting the common file or items obtained by
processing said common file.
A measurement is acquired in the following steps:
A signal appears at the input 4 of a path 1. This signal is applied to all
of the measurement ranges 9, and via the controllable selection means 16
to the module 5 for determining polarity and for limiting acquisition.
The module 5 for determining polarity and for limiting acquisition
determines the polarity of the signal and compares the value of the signal
with the threshold values, and in the event of the threshold values being
exceeded, it generates a trigger command which is applied to all of the
detect-and-hold modules 7, and to the control module 6 which begins a time
delay using the shift means 25.
During the time delay, the detect-and-hold modules 7 have enough time to
detect the peak value of the signal using their analog means 12. At the
end of the time delay, the control module 6 activates the digitizing
modules 13 so that they digitize the peak values of the signal.
During the time delay, or at the end thereof, the control module 6
generates an acquisition command for the reference path. This path
acquires, digitizes, and stores the number of the period, and the
polarized value of the reference voltage at that instant.
The automatic selection means 10 scan the measurement ranges in order of
decreasing gain and select the first digitized value which is less than
the saturation threshold of the measurement range from which it comes.
The control module 6 then causes the selected value to be stored, and then
reinitializes the modules to wait for a new signal.
In a first embodiment, known as a "burst" embodiment, the transfer step
occurs only at the end of a measurement campaign. This type of transfer
suffices whenever it is desired to make a spot check on an apparatus.
In a second embodiment, referred to as a "continuous" embodiment, the
transfer step takes place whenever there is a period of slack time between
two acquisitions occurring in a measurement campaign. This type of
transfer is necessary when an apparatus is under continuous surveillance
and when it is desired to be able to process acquisitions without
interrupting surveillance. This type of transfer is more effective in
predictive maintenance.
FIGS. 4A, 4B, 4C, and 4D show non-limiting examples of four possible
displays that can be used in the invention.
The first display shows an entire measurement campaign.
The system includes cursor means 35, 36 serving firstly to select any
particular period in the reference voltage for the measurement campaign,
and secondly to select a portion only of the measurement campaign.
The second display shows the amplitude and the polarity of discharges that
occurred during the period selected by the cursor 35 in the preceding
display.
The third display gives a list of predetermined parameters calculated on
the basis of the portion of the measurement campaign selected by the
cursors 36 in the first display.
The four display provides a diagram showing the occurrence of discharges as
a function of their amplitudes and phase offsets relative to the reference
voltage.
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